Life-history theory and management - Ecological Applications: Toward a Sustainable World - page 72

of these pressures. In this section I ask whether the varied situations have anything
in common. Are there, in fact, suites of species traits that seem to 'protect' native
species or, alternatively, that make them more likely to succumb to the pressures?
And are these traits the same as those that predict successful invasion or
restoration?
First, I consider cases where niche breadth and fl exibility play an important role
(Section 3.4.1) before turning to the many situations where the r / K concept again
seems to come into its own (Section 3.4.2). In a concluding section, the importance
of CSR traits, among others, will be considered (Section 3.4.3).

3.4.1 Niche breadth
and fl exibility -
freshwater and forest
at risk

Managers would be better able to prioritize species for conservation intervention if
it were possible to predict, on the basis of species traits, those most at risk of extinc-
tion. With this in mind Angermeier (1995) analyzed the traits of 197 native fresh-
water fi sh in Virginia, USA, paying special attention to the characteristics of the 17
species now extinct in Virginia and nine others considered at risk because their
ranges have shrunk signifi cantly. There has been a mix of human pressures at work,
from water abstraction for irrigation and the building of dams, through loss of
riverside vegetation, to pollution by agricultural and urban runoff.
Of particular interest is the greater vulnerability of ecological specialists in the
face of the various human pressures. A higher probability of local extinction attaches
to species whose niches include only one geological type (of several present in
Virginia), those restricted to fl owing water (as opposed to occurring in both fl ow-
ing and still water), and those with only one food category in their diet (i.e. wholly
piscivorous, insectivorous, herbivorous or detritivorous as opposed to omnivorous
on two or more food categories).
When it comes to vulnerability to extinction, do forest birds and freshwater
fi sh have something in common? In his study in a jarrah ( Eucalyptus marginata )
forest in southwestern Australia, Craig (2002) found that passerine species vary
considerably in the extent to which their populations are affected by selective
logging (where only high quality trees are removed). Western yellow robins
( Eopsaltria griseogularis ) and rufous treecreepers ( Climacteris rufa ) did not decline
after logging, unlike golden whistlers ( Pachycephala pectoralis ) and white-naped
honeyeaters ( Melithreptus lunatus ). Craig carefully assessed foraging behavior,
making observations in three seasons, in different subhabitats, and before and after
logging took place. He recorded foraging location (aerial, on the ground, associated
with living vegetation, dead logs, etc.), foraging height, and type of maneuver (glean,
hover, pounce, etc.).
The species that are least vulnerable to logging show much more fl exibility in
their foraging behavior, with both seasonal variation and changes in response to
logging. Thus, the robins (four changes) forage more on the ground and pounce
more in winter (than in other seasons) and also after logging. The treecreepers (four
changes) forage more on marri trees ( Corymbia calophylla , which coexist with the
jarrah trees), on horizontal surfaces and lower in the canopy in winter, and forage
more in forest gaps after logging. By contrast, each of the species that declined after
logging (whistlers and honeyeaters) only display a single variation in foraging
behavior. Craig recommends that unlogged buffer areas should be provided to safe-
guard the whistler and honeyeater populations. Greater behavioral fl exibility, which
we can equate with a broader niche, seems to buffer the robins and treecreepers